Work in this component has focused on determining whether immune-function assays can be used as biomarkers of exposure for a variety of toxicants and whether these assays can be modified to detect exposure to specific toxicants. Eight different toxicants were used to test the applicability of these assays, four metals (Hg, Cd, chromate and Ni) and four organics (benzoquinone, hydroquinone, styrene oxide and aroclor, a PCB). Applicability was assessed using both B-cell and T-cell mitogen assays and the mixed lymphocyte culture (MLC), a T-cell assay. Dose/response exposures were conducted in vitro with all eight toxicants using concentrations that spanned five orders of magnitude (100 ppm - 10 ppb). At the lowest concentration tested (10 ppb), all of the toxicants induced changes in at least one assay and all of the metals induced changes in at least two assays. Moreover at 10 ppb, all of the metals enhanced the proliferation of T-cells in the MLC. Because of the success with the metals in these dose/response studies, our next series of experiments focused on modifying these proliferation assays to detect in vivo exposures to specific metals and on understanding the mechanisms whereby metals alter lymphocyte proliferation. For these studies we employed rats exposed in vivo to either chromate or to cadmium. Using variants of the mitogen and MLC assays, cells isolated from rats exposed to chromate responded differently than cells isolated from rats exposed to cadmium. Moreover, in vivo cadmium exposure but not in vivo chromate exposure enhanced the antigenicity of splenocytes taken from exposed rats toward allogeneic splenocytes. Our results indicate that variants of these proliferation assays may be useful for detecting low-level exposures to chromate or cadmium and perhaps other metals as well. In the coming grant period we will focus on applying these assays (both the original assays and our variants) to humans exposed to chromate and to cadmium. In addition, we will continue investigations into how variants of these assays can be used as biomarkers of exposure for a wide variety of metals. We will also attempt to clone metal-responsive T-cells from both humans and animals exposed to chromate and cadmium. This has already been done with nickel- exposed individuals and we have evidence that chromate, and perhaps other metals, induce a subpopulation of metal responsive T-cells. Should the cloning experiments be successful, it would represent a powerful biomarker of metal exposure.